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In Reply to: Just opened up TDS Audiophile unit. posted by Jon L on April 09, 2002 at 09:59:31:
Could the TDS unit be just tranformer-based interface without the volume control? It would make sense...What the TDS is is basically a passive distortion generator. They use what amounts to poor quality transformers (which are being used more as autoformers since it provides no ground isolation) in order to produce the distortion. The result is a significant amount of third, fifth and seventh harmonic distortion (as well as a good amount of second harmonic), a rather large notch in the midrange and a big resonant spike at about 70 kHz.
I'm not saying this to slam TDS. I'm saying this because this is precisely what it was designed and intended to do. While their less than honest marketing literature denies this (i.e. specifically denying that the TDS is a distortion generator), they make no secret of this fact in their patent (5,361,306). From the abstract:
The present invention includes a field inducing coil through which input electronic audio signals are to be transmitted to set up an electromagnetic field. The field inducing coil is weakly coupled to an electromagnetic field receptor such that when an input electronic audio signal is transmitted through the inducing coil only a small portion of the electromagnetic field cuts or passes through the field receptor in order to produce an induced electronic audio signal having a greater harmonic content than the input electronic audio signal.
In their patent they describe how they built the prototype unit using the voice coils out of some replacement radio speakers from Radio Shack to produce a transformer with poor primary/secondary coupling in order to generate the distortion.
Basically, the reason you like the TDS so much is because of the distortion it adds to the signal and the signal it sucks out of the midrange via the notch and possibly any side-effects due to the high frequency resonance. It's also a good example of why I don't obsess over objective perfection. Sometimes the objectively worse result produces a better subjective result.
So don't take this post as criticism. The only thing I'm critical of with regard to TDS is the blatant dishonesty of some of their marketing claims.
se
Follow Ups:
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Do you mean how it sounds? First off, it gives you 6dB gain, so you gotta adjust your volumes to same level before A-B comparisons.You definitely hear a smoothing in that 1-3K "presence" region, likely down in level compared to "nothing," but with digital gear, it helps to smooth out some of the worse sibilances and poor recordings. Overall more vinyl or SACD-like presence region, good or bad.
There does seem to be a little more "bloom" in mid-bass. I like it, as bass is less sterile-sounding, but it can be less tight-sounding if your system already is on the loose side.
Most importantly, you get the feeling there is a LOT more harmonics through TDS. As Steve pointed out, these may be the added harmonic "distortions," but the effect is similar to switching from a good solid state amp to a good tubed one. More "pizzaz" to vocals with decays that last longer. More hall ambience, more overtones. It does sound less "linear," but once I take out the TDS, I'm much less involved with the music.
Yes, I do hear the "harmonic distortions," but I like'em. Sounds like harmonic distortions of some very fine tube amps to me. It also seems to provide ~3dB of gain, which I don't understand in a "passive" device. It's been awhile since I took it out of the system and maybe it's time to reevaluate again.Just curious, the specific "suckouts" and "peaks" you mention. Is that reported somewhere or have you measured?
Yes, I do hear the "harmonic distortions," but I like'em.And of course that's all that counts in my opinion. Might I offer you a free membership in the Hedonist Subjectivists Club? :)
Sounds like harmonic distortions of some very fine tube amps to me.
Yeah. As I've said in the past, if objective performance is all that matters, no one would touch something like a SET with a 10-foot pole. :)
It also seems to provide ~3dB of gain, which I don't understand in a "passive" device.
It's actually about 6dB. And it's able to do that in a passive device because it's using transformers which can provide voltage gain (or current gain, but not both simultaneously as they are passive devices and power out can be no greater than power in) depending on the turns ratio between the primary and secondary. I'm currently working on an integrated amplifier design that uses transformers to provide all of the voltage gain passively. If it pans out, I'll post a DIY piece on it here.
Just curious, the specific "suckouts" and "peaks" you mention. Is that reported somewhere or have you measured?
Martin Colloms did the measurements in his review of the TDS passive in the April 1999 issue of Hi-Fi News & Record Review. I'd post the frequency response and distortion plots but I'm not entirely sure that would fall under copyright fair use doctrine.
se
The gain is easy to explain - it's a step-up transformer. With line-level signals, volume is controlled by voltage, not power. In a transformer, input power is equal to output power (not counting losses, of course), but current and voltage can be changed. So, a step up transformer draws low voltage and high current, and converts it to higher voltage and lower current.I guess this means that this device would sound better when hooked up to a source that has good drive capabilities.
So, a step up transformer draws low voltage and high current, and converts it to higher voltage and lower current.Right. It all boils down to the square of the turns ratio. In a 1:2 step-up, the load the transformer is driving is reflected back to the source at 1/4th its value and the source impedance is reflected in the transformer's output impedance at four times its value. Not taking into account winding resistance of course.
se
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